This invention concerns a device for detecting an interface between two fluids of differing electrical properties.
It is often required to detect an interface between two fluids of differing electrical properties e.g. to detect the interface between the fuel and air in a fuel tank so as to determine the amount of fuel left in the tank. Such detection has in the past often been effected, as shown in U.S. Pat. Nos. 2,789,435 and 3,148,314, by employing a capacitative probe at short wave radio frequencies, the probe being inserted into the fuel tank and being connected in an electrical circuit which includes a meter for measuring the capacitance of the probe. As will be appreciated, the capacitance of the probe will alter according to whether the probe is fully immersed in the fuel, is partly immersed therein, or is not immersed in fuel at all. Such devices which rely on the measurement of capacitance, however, are not suitable for detecting an interface between liquids which form an emulsion with each other or where one of the liquids is an emulsion.
In all these known devices, moreover, the meter is affected by the capacitance between the probe and the tank, while the reading produced by the meter is affected not merely by the position of the interface but also by the electrical properties of the fluids forming the interface. In the known devices, moreover, contamination of the probe can make it difficult to determine the position of an interface, while a change in the fluids used or in the container used for such fluids involves re-calibration.
The object of the present invention is to overcome the above-mentioned disadvantages.